Pages 87-92 Epithelial Tissues Locations: Body coverings Body linings Glandular tissue Functions: Protection Absorption Filtration Secretion © 2015 Pearson Education, Inc. Epithelium Characteristics Cells fit closely together and often form sheets The apical surface is the free surface of the tissue The unattached surface Can be exposed to exterior or cavity of an organ The lower surface of the epithelium (the basal lamina) rests on a basement membrane Consists of reticular connective tissue secures upper layers © 2015 Pearson Education, Inc. Epithelium Characteristics Avascular (no blood supply) Relies on circulatory system to obtain food and oxygen Surrounding connective tissues supply via diffusion from nearby capillaries Regenerate easily if well nourished (through normal cell division) Cells on exterior of the skin are exposed to friction and other hostile substances and are sloughed off Classification of Epithelia Two name system: First name = # of layers Second name = shape of cells Named using number of cell layers: Simple—one layer Absorption/secretion/filtration are main functions Stratified—more than one layer Ideal for protection Often found where there is friction or abuse; durable © 2015 Pearson Education, Inc. Figure 3.17a Classification and functions of epithelia. Apical surface Basal surface Simple Apical surface Basal surface Stratified (a) Classification based on number of cell layers Epithelial shapes Names using shape of cells Squamous Flattened, like fish scales Cuboidal Cube-shaped, like dice Columnar Column-like © 2015 Pearson Education, Inc. Figure 3.17b Classification and functions of epithelia. Squamous Cuboidal Columnar (b) Classification based on cell shape Figure 3.17c Classification and functions of epithelia. Number of layers One layer: simple epithelial tissues More than one layer: stratified epithelial tissues Squamous Diffusion and filtration Secretion in serous membranes Protection Cuboidal Secretion and absorption; ciliated types propel mucus or reproductive cells Secretion and absorption; ciliated types propel mucus or reproductive cells Protection; these tissue types are rare in humans Cell shape Columnar Transitional Protection; stretching to accommodate distension of urinary structures (c) Function of epithelial tissue related to tissue type Remember these general characteristics and you will be able to classify each type a lot easier !! Pseudostratified Columnar Single layer some cells are shorter than others, giving a false (pseudo) impression of stratification © 2015 Pearson Education, Inc. Cilia Pseudostratified epithelial layer Pseudostratified epithelial layer Basement membrane Basement membrane Connective tissue (d) Diagram: Pseudostratified (ciliated) columnar Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (560×). Transitional Epithelium Unique because of its ability to become temporarily modified in arrangement and shape modified stratified squamous epithelium Can stretch and rebound Locations: urinary system organs © 2015 Pearson Education, Inc. Figure 3.18f Types of epithelia and their common locations in the body. Basement membrane Transitional epithelium Basement membrane Transitional epithelium Connective tissue (f) Diagram: Transitional Photomicrograph: Transitional epithelium lining of the bladder, relaxed state (270×); surface rounded cells flatten and elongate when the bladder fills with urine. Glandular Epithelium Two major gland types: Endocrine gland Ductless; secretions diffuse into blood vessels All secretions are hormones Examples include thyroid, adrenals, and pituitary Exocrine gland Secretions empty through ducts to the epithelial surface Include sweat and oil glands, liver (bile duct), and pancreas (digestive enzymes), mammary glands (milk) Includes both internal and external glands © 2015 Pearson Education, Inc.